Memorial official Oleg Orlov told Interfax on Wednesday the incident occurred in the early hours of Nov. 21.

"Stickers with the words 'foreign agent' were put near the Memorial plaque," he said.

"We have already reported the incident to the Tverskoy police station. We are asking for a criminal case to be opened on the basis of the article dealing with vandalism," Orlov said.

Memorial links the incident to the enactment of the law "on foreign agents" on Nov. 21. This law requires NGOs receiving foreign grants to register as "foreign agents."

In a statement obtained by Interfax, Memorial said this law is "immoral and illegal."

"Memorial continues to stand its ground: we have no intention of getting registered as 'a foreign agent.' We see the words written on the Memorial building as a deliberate insult of the memory of the millions of people who died in the GULAG," Memorial said.